  def bin_search(items, key):
      """折半查找"""
      start, end = 0, len(items) - 1
      while start <= end:
          mid = (start + end) // 2
          if key > items[mid]:
              start = mid + 1
          elif key < items[mid]:
              end = mid - 1
          else:
              return mid
      return -1